1. Field of the Invention
The present invention relates to a non-bolt joint structure and a method for producing the non-bolt joint structure.
2. Description of the Related Art
It is often the case that a welded joint welding pipes with each other in a construction field is used for connecting polyethylene pipes. There is, however, a variety of disadvantages when pipes are welded in the construction field.
Japanese Utility model Laid-Open No. 1-174690 referenced in International Search Report of PCT/JP2008/054767 on which the present application claims priority based, describes a joint connecting a polyethylene pipe and a metallic pipe with each other. The joint structure of this prior art is shown in FIG. 5A.
As shown in FIG. 5A, a metallic pipe 304 expands a flexible pipe 302. The flexible pipe 302 cuts into an inner circumference ditch portion 312 of a joint 301. Numerals 303 and 333 are packing rings for sealing.
However, unless the flexible pipe 302 is melted and gets soft, it is difficult for the flexible pipe 302 to cut into the inner circumference ditch portion 312 of the joint 301 with expanding the metallic pipe 304. Therefore, there is no record describing that this structure is employed.
As shown in FIG. 5B, Japanese Patent Laid-Open No. 11-201343 describes that steel pipes 401 and 402 are covered with a steel sleeve 403, and then diameters of the steel pipes 401, 402 and the steel sleeve 403 are expanded to be plastically deformed.
And, it also describes that a seal member such as a rubber ring is provided on each side of sleeves for improving cutoff performance.
That is, above two documents do not describe that the cross-sectional shape of the polyethylene pipe is curved as an arc with an inner ring.
Japanese Patent Laid-Open No. 2005-61549 describes that a joint connects a polyethylene pipe with a receiving opening section integrally being in communication with a valve casing.
Japanese Patent Laid-Open No. 11-201342 describes a connecting structure in which a resin header is connected with a metallic joint.
Japanese Patent Laid-Open No. 10-82487 describes a technique in which a pipe is nipped between both inner and outer sleeves.
U.S. Pat. No. 3,972,548 describes that a first pipe expanded its diameter of ends is fitted into a second pipe.
U.S. Pat. No. 4,805,945 describes a joint in which pressure is applied to an end of a tube from an inner side, and then the tube is tucked in a sleeve.
EP0139500A2 describes forming a bulge portion in the way that an end of a pipe is inserted into a pre-forming processed joint and then the end of the pipe is plastically deformed by such as a die.
Japanese Patent Laid-Open No. 2001-124278, 2005-61549, and 11-270763 describe a non-bolt joint structure.
An example of a non-bolt joint structure described above is described in FIG. 4.
In FIG. 4, a polyethylene pipe 102 is jointed to a metallic (FCD) first fluid conduit 101 being in communication with a valve casing 100.
In this conventional non-bolt joint structure, the metallic first fluid conduit 101 is jointed to the polyethylene pipe 102 in the way that an internal thread portion 103 is formed in an inner circumference of the first fluid conduit 101 while an external thread portion 104 is formed in an outer circumference of the polyethylene pipe 102, whereby the external thread portion 104 is threadably mounted on the internal thread portion 103. A numeral 105 describes an inner core.
However, in the conventional non-bolt joint structure, two pipes 101, 102 are jointed with each other by using a screw structure, thereby there is a need for casting a special polyethylene pipe having the screw structure.